The present invention relates broadly to servo systems, and in particular to an automatic bandwidth control system for an adaptive optics servo.
In general, a servo system by definition is a combination of elements for the control of a source of power in which the output of the system or some function of the output is fed back for comparison with the input and the difference between these quantities is used in controlling the power. With the advent of the laser, servo systems and optics have been combined for various system applications. One of which applications is controlling a laser to scan a target or an area to provide data thereabout. Such systems basically use the laser as an optical device to obtain information or data for various purposes. The servo portion of the system is utilized to maintain the laser on target and to provide optimum illumination of said target.
In system utilizing coherent optical adaptive techniques, speckle degradation is only one source of bandwidth degrations. Additional bandwidth-related problems that occur are caused by atmospheric turbulence, and interference between adjacent channels of multidither coherent optical adaptive techniques frequency channels. The fundamental problem is that the target irradiance which is produced by coherent optical adaptive techniques system, does vary with bandwidth. Furthermore, this variation is scenario dependent and therefore the severity of the irradiance, or Strehl ratio degradation which results from a given change in bandwidth can be either very severe or hardly noticeable. In order to maintain a high Strehl ratio for the turbulence scenario it is desirable to adjust the bandwidth to a high value in the vicinity of 1000 to 1200 Hz, whereas in the speckle scenario a very low bandwidth is desired. In the combined scenario a moderate bandwidth of about 600 to 800 Hz is the most desirable. The present invention automatically selects the optimum bandwidth for any scenario and keeps adjusting it as the scenario changes, always maintaining the highest Strehl ratio possible.